Revert "Core/Logging: Use logger cache for speed up logger filter search"

This reverts commit 39331ea7b9e906b67378a1be6c0c694d264eda3a.
This is required to fix a race condition introduced with the logger cache. Adding a locking mechanism might make worthless the speed gain added by the cache itself, push a proper thread-safe implementation if it's worth it.

Helgrind log:
Possible data race during write of size 8 at 0x736F428 by thread #1
Locks held: none
   at 0x11872DF: std::_Hashtable<std::string, std::pair<std::string const, Logger const*>, std::allocator<std::pair<std::string const, Logger const*> >, std::__detail::_Select1st, std::equal_to<std::string>, std::hash<std::string>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true> >::_M_insert_bucket_begin(unsigned long, std::__detail::_Hash_node<std::pair<std::string const, Logger const*>, true>*) (hashtable.h:1196)
   by 0x11865A1: std::_Hashtable<std::string, std::pair<std::string const, Logger const*>, std::allocator<std::pair<std::string const, Logger const*> >, std::__detail::_Select1st, std::equal_to<std::string>, std::hash<std::string>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true> >::_M_insert_unique_node(unsigned long, unsigned long, std::__detail::_Hash_node<std::pair<std::string const, Logger const*>, true>*) (hashtable.h:1342)
   by 0x1185A48: std::__detail::_Map_base<std::string, std::pair<std::string const, Logger const*>, std::allocator<std::pair<std::string const, Logger const*> >, std::__detail::_Select1st, std::equal_to<std::string>, std::hash<std::string>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true>, true>::operator[](std::string const&) (hashtable_policy.h:496)
   by 0x1184F3A: std::unordered_map<std::string, Logger const*, std::hash<std::string>, std::equal_to<std::string>, std::allocator<std::pair<std::string const, Logger const*> > >::operator[](std::string const&) (unordered_map.h:596)
   by 0x1184495: Log::GetLoggerByType(std::string const&) (Log.h:106)
   by 0x1184527: Log::ShouldLog(std::string const&, LogLevel) (Log.h:112)
   by 0x16E7121: World::LoadConfigSettings(bool) (World.cpp:909)
   by 0x16EB623: World::SetInitialWorldSettings() (World.cpp:1276)
   by 0x118F0EC: Master::Run() (Master.cpp:169)
   by 0x1196AFF: main (Main.cpp:142)

This conflicts with a previous read of size 8 by thread #3
Locks held: none
   at 0x1186EA6: std::_Hashtable<std::string, std::pair<std::string const, Logger const*>, std::allocator<std::pair<std::string const, Logger const*> >, std::__detail::_Select1st, std::equal_to<std::string>, std::hash<std::string>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true> >::_M_find_before_node(unsigned long, std::string const&, unsigned long) const (hashtable.h:1162)
   by 0x1186263: std::_Hashtable<std::string, std::pair<std::string const, Logger const*>, std::allocator<std::pair<std::string const, Logger const*> >, std::__detail::_Select1st, std::equal_to<std::string>, std::hash<std::string>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true> >::_M_find_node(unsigned long, std::string const&, unsigned long) const (hashtable.h:604)
   by 0x11857B9: std::_Hashtable<std::string, std::pair<std::string const, Logger const*>, std::allocator<std::pair<std::string const, Logger const*> >, std::__detail::_Select1st, std::equal_to<std::string>, std::hash<std::string>, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<true, false, true> >::find(std::string const&) (hashtable.h:1025)
   by 0x1184DE2: std::unordered_map<std::string, Logger const*, std::hash<std::string>, std::equal_to<std::string>, std::allocator<std::pair<std::string const, Logger const*> > >::find(std::string const&) (unordered_map.h:543)
   by 0x11842EF: Log::GetLoggerByType(std::string const&) (Log.h:84)
   by 0x1184527: Log::ShouldLog(std::string const&, LogLevel) (Log.h:112)
   by 0x189AACA: MySQLConnection::Execute(char const*) (MySQLConnection.cpp:175)
   by 0x18A3225: BasicStatementTask::Execute() (AdhocStatement.cpp:56)

Address 0x736F428 is 120 bytes inside a block of size 184 alloc'd
   at 0x4C2AE3A: operator new(unsigned long, std::nothrow_t const&) (vg_replace_malloc.c:350)
   by 0x1185046: ACE_Singleton<Log, ACE_Thread_Mutex>::instance() (Singleton.cpp:91)
   by 0x11968E2: main (Main.cpp:135)